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Numerical Models of Lithosphere Removal in the Sierra Nevada de Santa Marta, Colombia

  • Author / Creator
    Quiroga, David
  • The Sierra Nevada de Santa Marta (SNSM) in northern Colombia, is one of the highest coastal mountains
    in the world with a maximum height of more than 5.7 km. Geophysical measurements report that there
    is a high Bouguer gravity anomaly (>+130 mGal) in the region, indicating that the mountain does not
    have a crustal root. Previous studies attributed the support of the mountain to the underthrusting
    buoyant Caribbean plateau or to elastic stresses within the continental lithosphere. However, thermo-
    chronological studies report a recent uplift episode (in the last 2 Ma) that does not have a clear driving
    force. This thesis proposes that this region experienced a localized lithosphere removal event, whereby
    the dense lower lithosphere sank into the mantle as a drip, resulting a thin crust and lithosphere and
    causing surface uplift.
    To test this hypothesis, 2D and 3D numerical models are developed using the software ASPECT. The
    models examine the dynamics of a lithosphere drip and the associated observations, including surface
    topography, gravity anomaly and surface heat flow. The general model setup has a four-layer structure
    consisting of an upper crust, lower crust, mantle lithosphere and sublithosphere mantle. There is an
    initially thickened crust in the middle of the domain, representing the SNSM. This induces a perturbation
    in the lower lithosphere which is gravitationally unstable and undergoes foundering. The first 2D models
    are used to define a reference setup, by testing the effect of initial crustal root thickness, lateral
    compression rate, perturbation width, and plastic rheology parameters. Subsequent 2D models consist
    of modifications of the reference and explore the effects of crustal root eclogitization, lithosphere
    rheology, upper crustal density, initial crustal thickness, and lateral compression. In the preferred 2D
    model, the surface first undergoes subsidence, but post-removal non-isostatic forces induce uplift rates
    above 0.2 mm/yr for about 1 Ma, holding a region of high topography (3.3 km) and a positive Bouguer
    gravity anomaly of 103 mGal, consistent with SNSM observations. Additional calculations show that
    lithosphere removal generates a low seismic wave velocity anomaly under the Moho (-5% and -8% for
    Vs and Vp, respectively) and potentially inducing lower crustal and upper mantle melting. The final set
    of models uses a simplified 3D geometry to show that a 3D drip is wider and is associated with up to
    66% of less subsidence and positive gravity anomalies that are up to 112% higher than an equivalent 2D
    model.
    The models show that lithosphere removal is a viable explanation for the origin of the SNSM. The
    removal event could have occurred either very recently (< 2 Ma ago), potentially explaining a recent
    uplift episode, or earlier (50-40 Ma ago), possibly affecting the Paleocene-Eocene magmatism in this
    region. In either case, lithosphere removal would have affected the continental lithosphere structure.
    This work shows that local lithosphere geodynamics may have played an important role in the geological
    history of the SNSM, northern Colombia, and the Caribbean. The insights and quantitative predictions
    from the numerical models provide important constraints for future studies of this complex region.

  • Subjects / Keywords
  • Graduation date
    Spring 2022
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-6mk4-sj26
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.